Biting insects

Biting insects feed on humans and animals by piercing skin to tap into a blood vessel. They actively seek a food source by using their various senses such as heat, smell and sight to find a suitable host. Some insects make a quick feed and leave while others prefer to find hidden areas of the body to stay till they are gorged and can only drop off when they are swollen with blood.

Whichever way they find a host and feed, however, biting insects can cause itching, inflammation, painful welts and in addition can transmit many serious diseases that affect millions of people across the world.

Why do insect bites itch?

Bites itch because your body reacts to the saliva injected by the insect while it is biting you.

Biting insects have a complex mouth structure that varies between species. It can include a needle-like part that pierces the skin and other parts that are serrated and saw through the flesh to find a blood vessel.

They also have a food canal to suck up blood and a canal that injects saliva containing anticoagulant and anaesthetic. The anticoagulant keeps the blood liquid to keep it flowing and the anaesthetic stops you from feeling the bite so you don’t disturb the feeding insect.

The body’s immune system recognises the foreign material injected into the bite and produces histamine as a defence mechanism. This causes localised inflammation and itching.

The mouth parts of a female mosquito

Reactions to bites

People’s reactions to bites can vary greatly depending on the sensitivity of their immune system and whether they have been bitten before.

It can take hours or days for itching or redness to occur after being bitten, making it difficult to tell what bit you. In this case you will need other identifying factors to tell the source of the bite.

Fleas

Fleas are wingless insects that are about 3-4mm long when adult. They are very agile and especially good at jumping.

As a ratio of their size, fleas are one of the longest jumpers of any animal. They can quickly spread widely once inside a building.

There are several types of flea that affect humans, pets and animals and are common in the human environment. They tend to prefer a particular animal host, but will still bite to see if the host is suitable before dropping off.

Mosquitoes

There are over 3,500 known species of mosquito worldwide and a large number of these transmit diseases that affect more than 700 million people each year, causing at least two million deaths.

Female v. male mosquitoes

Only the female mosquitoes need a blood meal, having the specialised mouth parts that can penetrate animal skin, though they can also feed on sweet plant juices.

Male mosquito mouth parts are adapted only to feed on nectar and plant juices and cannot penetrate skin. It is the females that transmit diseases to humans and animals.

The female mosquito finds a host by sensing carbon dioxide in breath, perspiration and body odours, and tends to feed in the evening and night time, though there are notable exceptions.

Mosquito bites

Mosquito bites are characterised by itchy red bumps on the skin, with varying degrees of swelling, depending on the person’s immune response.

How to prevent mosquito bites:

Cover skin: wear long sleeves, trousers, footwear and hats.

Avoid bright colours: bright colours attract mosquitoes.

Avoid strong scents: strong scents such as perfumes and deodorants attract mosquitoes; Use insect repellents: use gels and sprays containing DEET or other repellent for applying to exposed skin; lighting insect repellent coils or citronella candles can help keep mosquitoes away from an area;

Avoid areas with still water: mosquitoes breed in slow moving or still/stagnant water, so removing these from around the home — even small containers — will reduce mosquito numbers by preventing their breeding.

Use mosquito nets for sleeping: when in remote or undeveloped areas these are a proven way to prevent bites while sleeping and they can also be impregnated with insecticide to kill the mosquitoes as they land on the net.

Bed Bugs

You are most likely to pick up bed bugs from a hotel, where they can crawl into luggage and clothing. They can also catch a ride in bedding and furniture and spread through buildings by crawling through holes in walls, such as for electrical wiring, or along pipe work.

Bed bug bites

Bed bugs tend to feed at night but will search for a host at any time if they are starved. They find a host through an array of sensors that can detect warmth, carbon dioxide and body odours.

Bed bugs feed for only 5-10 minutes until they become engorged with blood, if not disturbed and may spend less than 20 minutes on a host. After feeding, they return to their shelter.

How to spot bed bug bites

Small, flat, raised bumps on skin.

Several bites tend to appear in a line or row along an exposed area of the skin. This is usually the arm or leg.

Several groups of bed bug bites around the body could indicate multiple bed bugs feeding.

How to treat bed bug bites

Bed bugs do not carry diseases so the only treatment needed is to stop itching and rarely for inflammation. If the bites develop into very itchy bumps, general products available from a pharmacy to stop itching are suitable. For inflammation it is best to see a doctor who can prescribe the most suitable treatment. Many people do not react to bed bug bites so do not need any treatment.

How to prevent bed bug bites

If you are worried about bringing back bed bugs from your travels, then follow these steps to prevent bed bugs from entering your home and feeding upon you at night:

Leave luggage in your garage or bathroom. Bed bugs don’t like tiles or concrete, and it is easier to spot them on a hard surface compared to carpet.

If you are really worried take off your clothes in the garage or bathroom and place them straight into the wash.

Flies

Midges and gnats

The term midge and gnat is a very general term for a wide range of flies, including the Sand fly and Black fly. Most are aquatic during the larval stage.

Biting Flies

It is important to note that not all flies bite, some go about their day to day lives without the need to feast on humans. However there are a few fly species which rely on our blood to survive, these are:

Sandfly

Blackfly

Horse fly

Highland midge

How to treat fly bites

Wash the bite with soap and warm water.

Use and apply either antiseptic cream or spray to the area after washing.

Apply ice to the bite for 15 minutes, several times a day.

Avoid scratching so you don’t break the skin and cause and infection.

The bites of some flies such as horse flies can bleed. In this case a simple plaster applied after the bite has been washed would help. If the bleeding doesn’t stop on its own, you should see a doctor.

How to prevent fly bites

Avoid outdoor activities during the day when flies are more prevalent.

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Human Lice

Head Louse

The head louse, or nit, is a single species of small wingless insect, Pediculus humanus capitis, which feeds only on human blood and has its complete life cycle on the human scalp.

Lice cannot jump or fly but can crawl from person to person in close contact. Head lice commonly affect children, but anyone with hair can catch them.

Head lice are considered harmless as they are not known to carry any disease and are regarded more as a cosmetic problem. They do cause itching of the scalp and secondary infections can result from scratching.

Adults are up to 3mm long and grey in colour until they have fed on blood, after which they become reddish.

The females lay 3-4 eggs per day near the base of a hair shaft, gluing the eggs to the hair. The eggs are oval and less than 1mm in length. They are transparent until hatched, after which they appear white.

The eggs hatch in 6-9 days and the shell stays attached to the hair.

The six legs of the louse each have a claw on the end to grab onto hair.

Detecting head lice

They are commonly found in the hair behind the ears and at the nape of the neck.

The remains of the white egg cases can also be seen attached to hairs.

The lice can be combed out of the hair onto a piece of white paper using a special nit comb that has very closely-spaced teeth to trap the lice.

Treating head lice

Repeated use of a nit comb can remove the lice, but larger infestation may only be effectively removed with medicated shampoos or lotions available from pharmacies. These contain insecticide so should be used carefully, especially on children.

Body louse

The body louse (Pediculus humanus humanus) is indistinguishable from the head louse, but lives mainly in clothing, so the two types do not interbreed under normal conditions.

They are thought to have evolved from head lice around 100,000 years ago, which is about the time when humans invented clothing.

The adults are 2.5-3.5 mm long with six legs and grey body.

Eggs are laid on clothing and the skin, being found mainly around the waist and armpits.

The adults must regularly feed on blood and will die in a few days at room temperature if away from a host.

Prevention and treatment is to wash infected clothing at high temperature or destroy it.

Typhus

The body louse can spread the rickettisal diseases Epidemic typhus (Rickettsia prowazekii) and Murine typhus (Rickettsia typhi). Epidemic typhus has been responsible for millions of deaths throughout history especially in time of war among soldiers and prisoners.

How Typhus spreads
The louse picks up the disease by feeding on an infected person then when moving to another person excretes the organism in its faeces. The bacteria infect the host through the bite wound when the faeces and squashed lice are rubbed over the skin. It can also be inhaled in air-borne particles or enter the body rough the mucous membranes of the mouth and eyes.

Bartonellosis

The body louse was the principle means of the spread of the bacteria B. Quintana, the cause of trench fever during the First World War. It infected a large proportion of troops on both sides. In recent times it has been recorded worldwide: in Europe, North America, Africa, and China. Other biting insects can also spread the disease.

Crab or pubic louse

The crab louse (Pthirus pubis) feeds exclusively on blood and is only found on humans. It is distinct from the other two types of human louse in appearance, having a rounder and shorter body. It is usually found in pubic hair or other coarse hair such as eye lashes, beards and moustaches. It is mainly spread by close contact, sexual activity and shared use of towels, clothing and beds.

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The Triatomine bug carries the protozoan, Trypanosoma cruzi, which causes Chagas disease, also called American trypanosomiasis.

Chagas disease

It is classified by WHO as a neglected tropical disease, with 8 million people infected worldwide and an estimated 10,000 deaths caused by complications from the disease.

There are 150 species of the bug and more than 100 species of mammal carry the parasite, so it is considered impossible to completely eradicate the disease.

Originally a rural disease, socioeconomic changes, deforestation, rural migration and urbanisation have resulted in Chagas disease spreading more widely, according to WHO, and it is increasingly being detected in countries where it is non-endemic.

Nymphs and adult of the triatomine bug

Bites

Triatomine bugs bite exposed areas such as the face, but it is not the bite that transmits the disease. After feeding, the bug defecates, which carries the protozoan onto the skin.

When the person inadvertently wipes their skin this can carry the protozoan into the bite, other broken skin, or the eyes and mouth.

Both the male and female adults and nymphs are blood sucking and carry the parasite in their faeces.

Control

The bugs live in cracks and crevices of poorly constructed homes, where they hide during daylight and emerge at night to feed. Fresh faeces contains live parasites, so infection can also occur after touching a place where they have defecated.

Spraying house interiors with insecticide, plastering walls to fill in hiding places, bed nets and hand hygiene are all effective means of control.

An adult bug and a nymph

Photo: An adult bug and a nymph with clear defecation marks on the wall, in a house in Mexico.Source: WHO (Chagas disease campaign), Isaias Montilla.

Moths

Out of an estimated 160,000 species of moth there is only one genus, Calyptra, that can bite animals to drink their blood.

There are around 19 species of the moth, which are commonly called vampire moths, but just one species is known to have the ability to pierce human skin: Calyptra thalictri.

Unlike mosquitoes, only the male moth is known to have the ability to drink blood.

There are few reports of the moth biting humans and the only known case of the moth drinking human blood was in a test by the Russian scientist Vladimir Kononenko in 1999.

This species is native to areas as disparate as Indonesia, the Urals and southern Europe.

In 2007 several newspapers reported recordings in Finland and later in Sweden. It is not thought to pose any risk to humans.

Arachnids

Arachnids are a separate Class from insects in the classification of the animal kingdom, distinguishable by their eight legs and two body sections: the abdomen and cepahlothorax.

The group is easily distinguished from insects, which have six legs, three body sections (head, thorax and abdomen) and one pair of antennae. They are both in the Arthropod phylum, however, which consists of animals having an exoskeleton.

The arachnids have many members that can be pests of humans: the ticks, mites, scorpions and spiders.

Ticks

There are around 900 species of tick, all of which are parasites that feed on the blood of mammals, birds and less commonly reptiles and amphibians.

Habit

Ticks inhabit areas with long grass or heavy vegetation. They can sense a host by detecting breath, body odours, body heat, moisture and vibrations through a sensory organ in the first pair of legs.

Ticks do not seek a host but lie in wait, climbing up grass or onto the edge of leaves and hold up their front pair of legs to wait for a host to pass and latch onto — a posture called ‘questing’. They then crawl around the host looking for their preferred site to feed from, such as soft skin.

A tick on a blade of grass

A tick on a blade of grass with forelegs extended in the questing position.Source: Wikimedia Commons: Mcvoorhis
https://commons.wikimedia.org/wiki/File:20140704-TickWaitingOnGrassBlade-CentralMA-USA.JPG

How to prevent tick bites

In areas of known infestation you can take some measures to reduce the chance of tick infestation:

It is important to remove a tick properly so that you do not leave mouth parts behind in the skin, squeeze body fluid into the bite or cause it to regurgitate into the bite, which will increase the chance of infection.

How to remove ticks:

Wear gloves or using a cloth or tissue to prevent catching an infection from contact with the tick;

Use a pair of fine-tipped tweezers or commercial tick removal tool;

Grab the tick as close as possible to the skin, to include the mouth parts if possible;

Gently pull the tick straight out until the mouth parts are removed;

Wash your hands with soap and water;

Clean the bite area with soap and water or an antiseptic; and

Seek medical attention if you cannot remove all of the tick from the skin.

Do not:

twist the tick — this can break off the mouth parts and leave them in the skin;

use any substance, such as alcohol, gels, ointment or petroleum jelly to try and make the tick drop off as this could make the tick regurgitate into the bite and cause infection;

use a flame, which could also make the tick regurgitate, carrying diseases into the skin;

scratch the bite because this will increase the risk of infection and cause further swelling.

Tick diseases

Ticks can carry a variety of viruses, bacteria and protozoa, including several at the same time, which can make diagnosis and treatment difficult.

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Mites

Mites are are closely related to ticks. There are nearly 50,000 known species, mostly microscopic, occupying a very diverse range of habitats. Many are pests of plants and animals such as bees and birds, but very few affect humans.

The house dust mite does not feed directly on humans but on shed skin particles and pet dander. The shed skins and faeces can cause allergic reactions in some people, similar to hay fever, asthma and eczema.

Scabies

The scabies mite, Sarcoptes scabiei, is a parasitic mite about 0.5mm long that burrows into the outer layer of skin to feed on skin cells. It lays 10-25 eggs that hatch and emerge from the skin after 3-4 days to travel to another part of the body and repeat the cycle.

The infection results in itching caused by the body’s reaction to secretions from the mites. This can take up to eight weeks to appear.

Scabies is highly contagious. People living in the same household are likely to become infected easily.

The most common treatments for scabies are the pesticides permethrin, malathion and lindane. However, these can have side effects and should be used with advice from a medical professional.

Rickettsialpox

Rickettsialpox is caused by the bacteria Rickettsia akari, which can be carried by house-mouse mites. They will seek new hosts, including humans, when the mice die off naturally or as a result of pest control. Infection is transmitted by the bite of the mite.

Rickettsialpox is regarded as a mild disease that takes 2-3 weeks to recover from. The first symptom is a bump around the bite that appears about a week after the bite, which turns into black crusty scab.